The projects under study are designed to give an understanding of the manner in which granulopoiesis is regulated. The role of vascular endothelium is being studied utilizing short term endothelial cell cultures. The present project is evaluating the kinetics of granulocyte-monocyte macrophage colony stimulating activity production by both human and murine endothelium, along with various factors that may act to induce the endothelium to produce colony stimulating activity. The effect of mainpulating prostaglandin biosynthesis, the effects of lithium, lactoferrin and other substances which may be involved in the regulation of normal white cell production are being studied for their effects of vascular endothelium. In addition, the interaction of the endothelium with monocytes, lymphocytes and granulocytes is being evaluated with regard to the production of colony stimulating activity. Furthermore an attempt to characterize biochemically and functionally the colony stimulating activity produced by vascular endothelium is continuing.